The present invention relates generally to tracking control systems in magnetic recording and/or reproducing apparatuses and more particularly to a system which accomplishes tracking control in a manner such that the magnetic heads can accurately trace along a track on a magnetic tape, by accrately detecting the tracking error of the reproducing rotary magnetic head.
In recent years, in magnetic recording and/or reproducing apparatuses such as video tape recorders (VTR) of the helical scan type for home use, there has been a trend toward even higher densities of recording and reproducing, a aided by improvements in magnetic tapes. For example, by reducing the tape speed and track pitch to approximately 1/3 of their values as compared to the case of the conventional recording and/or reproducing capacity of 2 hours, for example, recording and reproducing of 6 hours can be carried out. Such long-duration recording and/or reproducing techniques are being reduced to practice. However, in the VTR for home use, in which the tape travel system is simplified in order to lower the cost, it is difficult to reproduce a magnetic tape having a reduced track pitch as mentioned above while positively maintaining the required tracking precision.
Furthermore, in a magnetic recording/reproducing apparatus capable of recording/reproducing for 2 hours, it is necessary to manipulate a tracking knob in order to cause the magnetic head to undergo accurate tracking along a track of the magnetic tape, when interchanged reproduction is performed with another apparatus. That is, in the case where there are (1) differences in the position of the control head, (2) differences in the height of the video head, and (3) skews in the video track, between the recording and reproducing apparatuses, optimal tracking state is not obtained, and hence maximum output cannot be obtained at the time of this interchanged reproduction.
For example, in the case where the distance L from the position where a video head which is mounted on the rotary drum begins to make contact with the magnetic tape to the position of the control head is longer than a standard value in the recorder, the tracking phase deviates. In this case, a control pulse is recorded by the control head at the lower edge of the magnetic tape. In a magnetic recording and/or reproducing apparatus capable of carrying out recording and reproducing of 6 hours, for example, the recording interval of the control pulse is 0.37 milli-meters, which is approximately 1/3 of the 1.11 milli-meters, obtained in the case of a conventional recording and reproducing of 2 hours.
In the case where the above distance L is not coincident with the standard value, it is necessary to adjust the tracking knob to delay the reproducing control signal by a required time to thereby carry out normal tracking. However, adjustment of the tracking knob requires an operation in which, as the reproduced picture is observed, the knob is finely adjusted in a manner such that noise is not generated, and this manipulation is complicated.
Furthermore, while the rotational control of the rotary drum and the rotating magnetic heads carried out by means of a drum servo-control by reproducing the above control pulses accomplishes a control function of a degree such as to maintain the relative positions of the corresponding positional relationship between each track and the rotating video heads, this rotational control, in the prior art, has not accomplished the functional of a so-called tracking control.
Accordingly, a new tracking control system in a magnetic recording and/or reproducing apparatus was proposed by an United States Patent Application of which assignee is the same as the assignee of the present application.
In this proposed tracking control system, there are provided recording means for recording a tracking reference signal by forming tracks together with an information signal which is to be recorded, every predetermined horizontal scanning period of the above information signal, as well as recording on a magnetic recording medium so that the tracking reference signal recording position of a certain track is at a position in front with respect to one track in the track longitudinal direction, and at a position at the rear with respect to the other track of the tracking reference signal recording position of each of the two adjacent tracks on both sides of the above certain track, discriminating means for gate-discriminating the relative phase with respect to the tracking reference signal reproduced from the above track which is to be scanned of the above tracking reference signal reproduced as cross-talk from the tracks adjacent to the above track which is to be scanned, by obtaining a gate pulse from the above tracking reference signal reproduced from the track which is to be scanned, of the signal reproduced by a magnetic head from the above magnetic recording medium, a differential amplifier which obtains a tracking error signal from the output signal of the above discriminating means, and control means for controlling the relative scanning phase of the above magnetic head with respect to the magnetic recording medium, by obtaining the average value component of the tracking error signal at each of the plurality of tracks, of the output tracking error signal of the differential amplifier. According to this proposed system, the scanning phase of the magnetic head can be controlled upon reproduction, and can employ a known servo circuit, which enables a tracking control with low cost and simple construction.
Especially upon interchanged reproduction, the troublesome operation of the tracking knob which was conventionally required is not necessary, and interchanged reproduction of high quality can be obtained positively in a stable manner, by a tracking servo loop of a closed-loop construction. Since the tracking control is performed by use of the average value component of the tracking error every plurality of tracks, the system is especially effective upon normal reproduction. Upon reproduction of a magnetic recording medium having a track pattern in which it comprises no guard band such as in azimuth recording, the system is effective because the cross-talk between the adjacent tracks can be used. Hence, desirable tracking control can be obtained upon reproduction of tracks having narrower track width for long-duration magnetic recording and/or recording of the high density type in use recently.
After further developing to reduce the above proposed system into practice, the present inventor found that there is a problem in that accurate detection of the tracking error cannot be performed in some cases. That is, at some frequencies of the tracking reference signal, the tracking reference signal of the adjacent track which should be reproduced as cross-talk is sometimes not reproduced although the tracking error exists, and furthermore, according to the tracking error, the signal level of the reference signal of the adjacent track reproduced as cross-talk sometimes becomes higher than the signal level of the reference signal reproduced from the track which is to be scanned.